Computerized tomography (CT) is a well-known method for reconstructing a three-dimensional object distribution from a series of two-dimensional projections obtained from a multiplicity of orientations (views) around the object. Typically, the irradiating beam emanates from a point source, rendering the projections conical. The object is conceptually divided into thin parallel slices individually reconstructed from corresponding slice projections. Projections of an entire slice are required for reconstructing the slice, i.e., the entire slice has to be irradiated.
For example, in many CT scanning systems, an X-ray fan beam is projected along a plane through a patient to a plurality of radiation detectors, which provide measurements of X-ray attenuation through the patient along radial lines defined by the X-ray source and the individual detectors. Measurements are made at a plurality of source positions or views around the patient to obtain sets of measurements representing sets of intersecting radiation beam paths. Reconstructing an image from its projections is implemented by various algorithms. For example, one of the algorithms used for such a reconstruction incorporates spatial filtering of the projections and back projecting the filtered data into the image domain. The image plane (in the two-dimensional case) is divided into small square cells (of width in the order of millimeters) called pixels. The back-projection algorithm associates a detector number with each pixel in the field of view. The back-projection formula also adjusts the detector measurements for each pixel as a function of the distance of the pixel from the source of radiation. These adjustment factors are called weight factors. A back projected image is formed by summing the spatially filtered contribution of detector data for each pixel for all the views. Three-dimensional reconstructions from two-dimensional projections use a methodology similar to that of two-dimensional reconstructions from one-dimensional projections.
Prior art diagnostic CT scanners are stationary devices placed in dedicated rooms. Utilizing CT scanners as a part of a treatment procedure is time consuming and cumbersome. Prior art mobile systems are operable to provide real-time scanning and reconstruction during treatment. Such systems are aimed at reconstructing entire slices and therefore incorporate large x-ray detectors for acquiring entire slices projections.